Per-protocol data unit delivery-path indication

ABSTRACT

Indication of delivery-path information may benefit various communication systems. For example, wireless communication systems may benefit from per-protocol data unit delivery-path indication to data recipient or from setting a timer expiry value dependent on such received information. A method can comprise sending, by a data-sending protocol entity, a control protocol data unit. The control protocol data unit can identify protocol data units destined to a data-receiving protocol entity. The method can also comprise providing in the control protocol data unit, for each of the identified protocol data units, a direct or indirect indication of at least one delay figure of a delivery path chosen for an initial transmission of the identified protocol data unit.

BACKGROUND

Field

Indication of delivery-path information may benefit variouscommunication systems. For example, wireless communication systems maybenefit from per-protocol data unit delivery-path indication to datarecipient.

Description of the Related Art

In the Evolved Universal Terrestrial Radio Access Network (E-UTRAN)air-interface protocol stack, the Packet Data Convergence Protocol(PDCP) currently lies above the Radio Link Control (RLC) protocol. PDCPis currently defined by third generation partnership project (3GPP)technical specification (TS) 36.323, which is hereby incorporated hereinby reference. RLC is defined by 3GPP TS 36.322, which is herebyincorporated herein by reference.

For PDCP, the listed ‘Services expected from lower layers’ compriseamong others: acknowledged data transfer service, including indicationof successful delivery of PDCP PDUs.

The RLC protocol [TS 36.322] uses the reordering timer, withRRC-configurable expiry time, to infer when a packet has been lost atMAC layer instead of still undergoing possible HARQ retransmissions: thetimer is started when a gap in received PDUs is observed, and if thetimer expires the lost packet is NACKed to the peer RLC entity(acknowledged mode), or the gap in packets is ignored when deliveringdata to higher layer (unacknowledged mode).

Related to studies on dual connectivity in E-UTRAN, FIG. 1 illustratesdistributed radio link control and independent radio link controloptions. As shown in FIG. 1, in a distributed radio link control model,the RLC PDUs are assigned by the macro eNB and a subset is sent to thepico eNB. The RLC acknowledged mode PDU resegmentation mechanism, usedby Rel-10 for RLC retransmissions, is repurposed at the slave eNB to fitAMD PDU segments into the scheduled transport block. Moreover, RLCretransmissions may only be handled at the macro eNB.

In an independent-RLCs model, distinct RLC entities at macro and picohandle different sub-bearers. Moreover, UE protocol architecture isdifferent from Rel-10 CA.

Moreover, with respect to the independent-RLCs option, the master nodemay be provided the following feedback: whether each PDCP PDU wasreceived by the slave node over the “X2” interface; and which PDCP PDUsthe UE has indicated as successfully received to know which packets thenetwork-side PDCP can discard.

The above will be provided if the following feedback mechanisms are inplace: acknowledged data transfer over the “X2” interface, which is notpresent in the current data transfer over X2: see 3GPP technicalspecification (TS) 36.424); acknowledged data transfer over each of theRLC bearers serving the PDCP bearer, as currently specified in the RLCprotocol; and the indications of successful downlink delivery of PDCPPDUs, from the slave node to the master node.

Alternatively, a continuously running ARQ mechanism can be adopted atPDCP level, which is not currently in place in the PDCP protocol, whichmay render all three items above unnecessary. This also implies that theRLC bearers serving the acknowledged-mode PDCP bearer could run inunacknowledged mode.

SUMMARY

According to certain embodiments, a method comprises sending, by adata-sending protocol entity, a control protocol data unit. The controlprotocol data unit identifies other protocol data units destined to adata-receiving protocol entity. The method also comprises providing inthe control protocol data unit, for each of the identified protocol dataunits, a direct or indirect indication of at least one delay figure of adelivery path chosen for an initial transmission of the identifiedprotocol data unit.

In certain embodiments, an apparatus comprises at least one processorand at least one memory including computer program code. The at leastone memory and the computer program code are configured to, with the atleast one processor, cause the apparatus at least to send, by adata-sending protocol entity, a control protocol data unit. The controlprotocol data unit identifies other protocol data units destined to adata-receiving protocol entity. The at least one memory and the computerprogram code are also configured to, with the at least one processor,cause the apparatus at least to provide in the control protocol dataunit, for each of the identified protocol data units, a direct orindirect indication of at least one delay figure of a delivery pathchosen for an initial transmission of the identified protocol data unit.

An apparatus, according to certain embodiments, comprises sending meansfor sending, by a data-sending protocol entity, a control protocol dataunit. The control protocol data unit identifies other protocol dataunits destined to a data-receiving protocol entity. The apparatus alsocomprises providing means for providing in the control protocol dataunit, for each of the identified protocol data units, a direct orindirect indication of at least one delay figure of a delivery pathchosen for an initial transmission of the identified protocol data unit.

A non-transitory computer-readable medium is, in certain embodiments,encoded with instructions that, when executed in hardware, perform aprocess. The process comprises sending, by a data-sending protocolentity, a control protocol data unit. The control protocol data unitidentifies other protocol data units destined to a data-receivingprotocol entity. The process also comprises providing in the controlprotocol data unit, for each of the identified protocol data units, adirect or indirect indication of at least one delay figure of a deliverypath chosen for an initial transmission of the identified protocol dataunit.

A computer program, according to certain embodiments, comprising programinstructions which, when loaded into the apparatus, cause a computersystem to perform a process. The process comprises sending, by adata-sending protocol entity, a control protocol data unit. The controlprotocol data unit identifies other protocol data units destined to adata-receiving protocol entity. The process also comprises providing inthe control protocol data unit, for each of the identified protocol dataunits, a direct or indirect indication of at least one delay figure of adelivery path chosen for an initial transmission of the identifiedprotocol data unit.

According to certain embodiments, a method comprises receiving, from adata-sending protocol entity, a control protocol data unit. The controlprotocol data unit identifies other protocol data units destined to adata-receiving protocol entity. The method also comprises retrievingfrom the control protocol data unit, for at least one of the identifiedprotocol data units, a direct or indirect indication of at least onedelay figure of a delivery path chosen for an initial transmission ofthe identified protocol data unit. The method further comprises applyingthe at least one delay figure to determine a waiting time in relation toa gap in received protocol data units.

In certain embodiments, an apparatus comprises at least one processorand at least one memory including computer program code. The at leastone memory and the computer program code are configured to, with the atleast one processor, cause the apparatus at least to receive, from adata-sending protocol entity, a control protocol data unit. The controlprotocol data unit identifies other protocol data units destined to adata-receiving protocol entity. The at least one memory and the computerprogram code are also configured to, with the at least one processor,cause the apparatus at least to retrieve from the control protocol dataunit, for at least one of the identified protocol data units, a director indirect indication of at least one delay figure of a delivery pathchosen for an initial transmission of the identified protocol data unit.The at least one memory and the computer program code are furtherconfigured to, with the at least one processor, cause the apparatus atleast to apply the at least one delay figure to determine a waiting timein relation to a gap in received protocol data units.

An apparatus, according to certain embodiments, comprises receivingmeans for receiving, from a data-sending protocol entity, controlprotocol data unit. The control protocol data unit identifies otherprotocol data units destined to a data-receiving protocol entity. Theapparatus also comprises retrieving means for retrieving from thecontrol protocol data unit, for at least one of the identified protocoldata units, a direct or indirect indication of at least one delay figureof a delivery path chosen for an initial transmission of the identifiedprotocol data unit. The apparatus further comprises applying means forapplying the at least one delay figure to determine a waiting time inrelation to a gap in received protocol data units.

A non-transitory computer-readable medium is, in certain embodiments,encoded with instructions that, when executed in hardware, perform aprocess. The process comprises receiving, from a data-sending protocolentity, control protocol data unit. The control protocol data unitidentifies other protocol data units destined to a data-receivingprotocol entity. The process also comprises retrieving from the controlprotocol data unit, for at least one of the identified protocol dataunits, a direct or indirect indication of at least one delay figure of adelivery path chosen for an initial transmission of the identifiedprotocol data unit. The process further comprises applying the at leastone delay figure to determine a waiting time in relation to a gap inreceived protocol data units.

A computer program, in certain embodiments, comprising programinstructions which, when loaded into the apparatus, cause a computersystem to perform a process. The process comprises receiving, from adata-sending protocol entity, control protocol data unit. The controlprotocol data unit identifies other protocol data units destined to adata-receiving protocol entity. The process also comprises retrievingfrom the control protocol data unit, for at least one of the identifiedprotocol data units, a direct or indirect indication of at least onedelay figure of a delivery path chosen for an initial transmission ofthe identified protocol data unit. The process further comprisesapplying the at least one delay figure to determine a waiting time inrelation to a gap in received protocol data units.

BRIEF DESCRIPTION OF THE DRAWINGS

For proper understanding of the invention, reference should be made tothe accompanying drawings, wherein:

FIG. 1 illustrates distributed radio link control and independent radiolink control options.

FIG. 2 illustrates a method according to certain embodiments.

FIG. 3 illustrates another method according to certain embodiments.

FIG. 4 illustrates a system according to certain embodiments.

DETAILED DESCRIPTION

Certain embodiments may be applicable both to a distributed-RLC optionand to an independent-RLCs option. In certain embodiments, it is assumedthat automatic repeat request (ARQ) at PDCP is being used, in which casea timer, such as a reordering timer, can be used at PDCP to infer packetlosses as with RLC.

In certain embodiments, it is assumed that a data-sending protocolentity can choose for each packet sent, one of more than one deliverypaths each with different expected delay for the packet to come through.For example, the delay of sending a packet through the slave node mayexceed that of direct transmission from the master node at least by the“X2”-transfer delay. Moreover, the data-receiving protocol entity canuse a mechanism like RLC's timer to infer when a PDU has really beenlost in transfer at the lower protocol layer.

In the distributed-RLC option, the protocol of interest may be RLC. Inthe independent-RLCs option, the protocol of interest may be PDCP.

In such a scenario, when the data-receiving protocol entity observes agap in the sequence of received PDUs, the data-receiving protocol entitydoes not know much about the worst-case transmission-delaydifference(s), including components such as “X2”-transfer delay and HARQretransmissions at MAC, between the missing PDU(s) and the received PDUthat created the reception gap, to infer when that missing PDU(s) hasbeen lost in transfer at the lower protocol layer. As a result, packetsgone missing at the lower layer can only be NACKed by the receiving sideto the sending side (in the case of acknowledged-mode data transfer), orignored in the delivery of SDUs to higher layer (in the case ofunacknowledged-mode data transfer) under worst-of-worst caseassumptions, which then appears as longer-than-necessary transmissiondelay to the higher protocol layer to which the PDUs are eventuallydelivered.

Certain embodiments provide a per-PDU delivery-path indication to datarecipient and certain embodiments provide a timer expiry value based onsuch indications.

Providing a per-PDU delivery-path indication to data recipient canentail the data-sending protocol entity sending control PDUs, each ofwhich identifies other PDUs, for example by their SNs, destined to thedata-receiving protocol entity. The control PDUs can also identify, foreach identified PDU, a direct or indirect indication of at least onedelay figure, for example the best-case delay and the worst-case delay,of the delivery path chosen for the initial transmission of that PDU. Anexample of indirect indication is the lower-layer protocol-bearer, ifRLC, or protocol-connection, if MAC, through which that PDU was, or willbe, sent, in which case the associated delay figures for those pathshave been previously configured by RRC at bearer configuration.

Certain embodiments provide timer expiry value based on such delayvalues. In general, there are at least two PDUs involved when the timeris started: the PDU received that created a gap in the sequence ofreceived PDUs, and the one or more missing PDUs within that newlyappeared gap. The second component of this invention is that the expiryvalue of the timer started in such a situation depends on at least onedelay figure previously indicated for at least one of the involved PDUs.If none are available, a worst-case value can be used. The worst-casevalue can be a longest conceivable expiry value.

Various implementations are possible. For example, at bearerconfiguration, a best-case associated minimum delay D1 and worst-caseassociated maximum delay D2 can be configured by RRC to each lower-layerprotocol-bearer, if RLC, or protocol-connection, if MAC, delivering datafor this bearer.

When the timer is started, the expiry value can be the maximum, over allmissing PDUs i in the observed reception gap, of D2(i)−D1 (the PDUreceived that created the gap), where the ‘Dx’ of each PDU is determinedfrom a previously received delivery-path indication. If either or bothof the associated D1, D2 are unavailable, the longest of the configuredD2s and the shortest of the configured D1s can be used in thisdetermination as needed.

FIG. 2 illustrates a method according to certain embodiments. As shownin FIG. 2, a method can comprise at a transmitting side, at 310,regularly or irregularly sending, by a data-sending protocol entity, acontrol protocol data unit. The control protocol data unit can identifyprotocol data units destined to a data-receiving protocol entity. Thecontrol protocol data unit can identify the protocol data units by, forexample, sequence number.

The method can also comprise, at 320, providing in the control protocoldata unit, for each identified protocol data units, a direct or indirectindication of at least one delay figure of a delivery path chosen for aninitial transmission of the identified protocol data unit. The at leastone delay figure can comprise at least one of a best-case delay and aworst-case delay.

The method can also comprise at a receiving side, at 330, determining anexpiry value of a timer based on at least one delay figure previouslyindicated for at least one protocol data unit. The at least one protocoldata unit can comprise at least one of a missing protocol data unitwithin a gap and a received protocol data unit that created the gap.

The method can further comprise, at 340, determining an expiry value ofa timer based on a worst-case value of the at least one delay figure.The at least one delay figure can comprise at least one of apreconfigured best-case minimum delay and a preconfigured worst-casedelay, wherein the at least one delay figure is preconfigured at bearerconfiguration. The at least one delay figure can comprise a maximumdelay of all missing protocol data units in a gap and a minimum delay ofa received protocol data unit that created the gap.

FIG. 3 illustrates a method according to certain embodiments. As shownin FIG. 3, a method can comprise, at 410, regularly or irregularlyreceiving, from a data-sending protocol entity, a control protocol dataunit. The control protocol data unit can identify protocol data unitsdestined to a data-receiving protocol entity. The control protocol dataunit can identify the protocol data units by, for example, sequencenumber.

The method can also comprise, at 420, retrieving from the controlprotocol data unit, for at least one identified protocol data unit (forexample, for each identified protocol data unit), a direct or indirectindication of at least one delay figure of a delivery path chosen for aninitial transmission of the identified protocol data unit. The at leastone delay figure can comprise at least one of a best-case delay and aworst-case delay.

The method can further comprise, at 430, applying the at least one delayfigure to determine a waiting time in relation to a gap in receivedprotocol data units.

The method can also comprise, at 440, determining an expiry value of atimer based on at least one delay figure previously indicated for atleast one protocol data unit. The at least one protocol data unit cancomprise at least one of a missing protocol data unit within a gap and areceived protocol data unit that created the gap.

The method can further comprise, at 450, determining an expiry value ofa timer based on a worst-case value of the at least one delay figure.The at least one delay figure can comprise at least one of apreconfigured best-case minimum delay and a preconfigured worst-casedelay, wherein the at least one delay figure is preconfigured at bearerconfiguration. The at least one delay figure can comprise a maximumdelay of all missing protocol data units in a gap and a minimum delay ofa received protocol data unit that created the gap.

FIG. 4 illustrates a system according to certain embodiments of theinvention. It should be understood that each block of the flowchart ofFIG. 2 or 3 and any combination thereof may be implemented by variousmeans or their combinations, such as hardware, software, firmware, oneor more processors and/or circuitry. In one embodiment, a system maycomprise several devices, such as, for example, network element 510 anduser equipment (UE) or user device 520. The system may comprise morethan one UE 520 and more than one network element 510, although only oneof each is shown for the purposes of illustration. A network element canbe an access point, a base station, an eNode B (eNB), server, host, orany of the other network elements discussed herein. Each of thesedevices may comprise at least one processor or control unit or module,respectively indicated as 514 and 524. At least one memory may beprovided in each device, and indicated as 515 and 525, respectively. Thememory may comprise computer program instructions or computer codecontained therein. One or more transceiver 516 and 526 may be provided,and each device may also comprise an antenna, respectively illustratedas 517 and 527. Although only one antenna each is shown, many antennasand multiple antenna elements may be provided to each of the devices.Other configurations of these devices, for example, may be provided. Forexample, network element 510 and UE 520 may be additionally configuredfor wired communication, in addition to wireless communication, and insuch a case antennas 517 and 527 may illustrate any form ofcommunication hardware, without being limited to merely an antenna.Likewise, some network elements 510 may be solely configured for wiredcommunication, and such cases antenna 517 may illustrate any form ofwired communication hardware, such as a network interface card.

Transceivers 516 and 526 may each, independently, be a transmitter, areceiver, or both a transmitter and a receiver, or a unit or device thatmay be configured both for transmission and reception. The transmitterand/or receiver (as far as radio parts are concerned) may also beimplemented as a remote radio head which is not located in the deviceitself, but in a mast, for example.

It should also be appreciated that according to the “liquid” or flexibleradio concept, the operations and functionalities may be performed indifferent entities, such as nodes, hosts or servers, in a flexiblemanner. In other words, “division of labour” may vary case by case. Onepossible use is to make a network element to deliver local content. Oneor more functionalities may also be implemented as a virtual applicationthat is as software that can run on a server.

A user device or user equipment may be a mobile station (MS) such as amobile phone or smart phone or multimedia device, a computer, such as atablet, provided with wireless communication capabilities, personal dataor digital assistant (PDA) provided with wireless communicationcapabilities, portable media player, digital camera, pocket videocamera, navigation unit provided with wireless communicationcapabilities or any combinations thereof.

In an exemplary embodiment, an apparatus, such as a node or user device,may comprise means for carrying out embodiments described above inrelation to FIG. 2 or 3. Processors 514 and 524 may be embodied by anycomputational or data processing device, such as a central processingunit (CPU), application specific integrated circuit (ASIC), orcomparable device. The processors may be implemented as a singlecontroller, or a plurality of controllers or processors.

For firmware or software, the implementation may comprise modules orunit of at least one chip set, for example, procedures, functions, andso on.

Memories 515 and 525 may independently be any suitable storage device,such as a non-transitory computer-readable medium. A hard disk drive(HDD), random access memory (RAM), flash memory, or other suitablememory may be used. The memories may be combined on a single integratedcircuit as the processor, or may be separate therefrom. Furthermore, thecomputer program instructions may be stored in the memory and which maybe processed by the processors can be any suitable form of computerprogram code, for example, a compiled or interpreted computer programwritten in any suitable programming language. The memory or data storageentity is typically internal but may also be external or a combinationthereof, such as in the case when additional memory capacity is obtainedfrom a service provider. The memory may be fixed or removable.

The memory and the computer program instructions may be configured, withthe processor for the particular device, to cause a hardware apparatussuch as network element 510 and/or UE 520, to perform any of theprocesses described above (see, for example, FIGS. 2 and 3). Therefore,in certain embodiments, a non-transitory computer-readable medium may beencoded with computer instructions or one or more computer program (suchas added or updated software routine, applet or macro) that, whenexecuted in hardware, may perform a process such as one of the processesdescribed herein. Computer programs may be coded by a programminglanguage, which may be a high-level programming language, such asobjective-C, C, C++, C#, Java, etc., or a low-level programminglanguage, such as a machine language, or assembler. Alternatively,certain embodiments of the invention may be performed entirely inhardware.

Furthermore, although FIG. 4 illustrates a system including a networkelement 510 and a UE 520, embodiments of the invention may be applicableto other configurations, and configurations involving additionalelements, as illustrated and discussed herein. For example, multipleuser equipment devices and multiple network elements may be present, orother nodes providing similar functionality, such as nodes that combinethe functionality of a user equipment and an access point, such as arelay node.

One having ordinary skill in the art will readily understand that theinvention as discussed above may be practiced with steps in a differentorder, and/or with hardware elements in configurations which aredifferent than those which are disclosed. Therefore, although theinvention has been described based upon these preferred embodiments, itwould be apparent to those of skill in the art that certainmodifications, variations, and alternative constructions would beapparent, while remaining within the spirit and scope of the invention.In order to determine the metes and bounds of the invention, therefore,reference should be made to the appended claims.

GLOSSARY

-   ACK Positive acknowledgement-   AM Acknowledged Mode-   NACK Negative acknowledgement-   RLC Radio Link Control-   PDCP Packet Data Convergence Protocol-   PDU Protocol Data Unit-   SN Sequence Number-   UM Unacknowledged Mode

I claim:
 1. A method, comprising: choosing, by a data-sending protocolentity, for an initial transmission of at least one protocol data unit,one of more than one delivery paths each with different delay figuresfor the at least one protocol data units to come through to adata-receiving protocol entity; sending, a control protocol data unit,wherein said control protocol data unit identifies the at least oneprotocol data units destined to the data-receiving protocol entity; andproviding in the control protocol data unit, for each of the at leastone identified protocol data units, an indirect indication of at leastone delay figure of the delivery path chosen for the initialtransmission of the identified at least one protocol data unit.
 2. Themethod of claim 1, wherein the control protocol data unit identifies theother protocol data units by sequence number.
 3. The method of claim 1,wherein the at least one delay figure comprises at least one of abest-case delay and a worst-case delay.
 4. The method of claim 1,wherein the at least one delay figure comprises at least one of apreconfigured best-case minimum delay and a preconfigured worst-casedelay, wherein the at least one delay figure is preconfigured at bearerconfiguration.
 5. An apparatus, comprising: at least one processor; andat least one memory including computer program code, wherein the atleast one memory and the computer program code are configured to, withthe at least one processor, cause the apparatus at least to choose, by adata-sending protocol entity, for an initial transmission of at leastone protocol data unit, one of more than one delivery paths each withdifferent delay figures for the at least one protocol data units to comethrough to a data-receiving protocol entity; send, a control protocoldata unit, wherein said control protocol data unit identifies the atleast one protocol data units destined to the data-receiving protocolentity; and provide in the control protocol data unit, for each of theat least one identified protocol data units, an indirect indication ofat least one delay figure of the delivery path chosen for the initialtransmission of the identified at least one protocol data unit.
 6. Theapparatus of claim 5, wherein the control protocol data unit identifiesthe other protocol data units by sequence number.
 7. The apparatus ofclaim 5, wherein the at least one delay figure comprises at least one ofa best-case delay and a worst-case delay.
 8. The apparatus of claim 5,wherein the at least one delay figure comprises at least one of apreconfigured best-case minimum delay and a preconfigured worst-casedelay, wherein the at least one delay figure is preconfigured at bearerconfiguration.
 9. A method, comprising: receiving, from a data-sendingprotocol entity, a control protocol data unit, wherein said controlprotocol data unit identifies other protocol data units destined to adata-receiving protocol entity; retrieving from the control protocoldata unit, for at least one of said identified protocol data units, anindirect indication of at least one delay figure of a delivery pathchosen for an initial transmission of the identified protocol data unit,wherein the at least one delay figure is preconfigured at bearerconfiguration; observing a gap in a sequence of the identified otherprotocol data units at reception; and applying the at least one delayfigure to determine a waiting time in relation to the gap.
 10. Themethod according to claim 9, wherein the at least one delay figurecomprises at least one of a best-case delay and a worst-case delay. 11.The method according to claim 9, further comprising: using a timer forcontrolling the waiting time, and determining an expiry value of thetimer based on at least one delay figure previously indicated for atleast one protocol data unit.
 12. The method according to claim 9,wherein the at least one delay figure comprises a maximum delay of allmissing protocol data units in the gap and a minimum delay of a receivedprotocol data unit that created the gap.
 13. The method according toclaim 9, further comprising: using a timer for controlling the waitingtime, and determining an expiry value of the timer based on at least onedelay figure previously indicated for at least one protocol data unit,wherein the at least one protocol data unit comprises at least one of aprotocol data unit whose reception created a gap in the sequence ofreceived protocol data units, and a not-received protocol data unitwithin said gap.
 14. An apparatus, comprising: at least one processor;and at least one memory including computer program code, wherein the atleast one memory and the computer program code are configured to, withthe at least one processor, cause the apparatus at least to receive,from a data-sending protocol entity, a control protocol data unit, saidcontrol protocol data unit identifies other protocol data units destinedto a data-receiving protocol entity; retrieve from the control protocoldata unit, for at least one of said identified protocol data units, anindirect indication of at least one delay figure of a delivery pathchosen for an initial transmission of the identified protocol data unit,wherein the at least one delay figure is preconfigured at bearerconfiguration; observe a gap in a sequence of the identified otherprotocol data units at reception; and apply the at least one delayfigure to determine a waiting time in relation to the gap.
 15. Theapparatus according to claim 14, wherein the at least one delay figurecomprises at least one of a best-case delay and a worst-case delay. 16.The apparatus according to claim 14, wherein the at least one memory andthe computer program code are configured to, with the at least oneprocessor, cause the apparatus at least to: use a timer for controllingthe waiting time, and determine an expiry value of the timer based on atleast one delay figure previously indicated for at least one protocoldata unit.
 17. The apparatus according to claim 14, wherein the at leastone delay figure comprises a maximum delay of all missing protocol dataunits in a gap and a minimum delay of a received protocol data unit thatcreated the gap.
 18. The apparatus according to claim 14, wherein the atleast one memory and the computer program code are configured to, withthe at least one processor, cause the apparatus at least to: use a timerfor controlling the waiting time, and determine an expiry value of thetimer based on at least one delay figure previously indicated for atleast one protocol data unit, wherein the at least one protocol dataunit comprises at least one of a protocol data unit whose receptioncreated a gap in the sequence of received protocol data units, and anot-received protocol data unit within said gap.
 19. A non-transitorycomputer-readable medium encoded with instructions that, when executedin hardware, perform a process comprising: choosing, by a data-sendingprotocol entity, for an initial transmission of at least one protocoldata unit, one of more than one delivery paths each with different delayfigures for the at least one protocol data units to come through to adata-receiving protocol entity; sending, a control protocol data unit,wherein said control protocol data unit identifies the at least oneprotocol data units destined to the data-receiving protocol entity; andproviding in the control protocol data unit, for each of the at leastone identified protocol data units, an indirect indication of at leastone delay figure of the delivery path chosen for the initialtransmission of the identified at least one protocol data unit.
 20. Anon-transitory computer-readable medium encoded with instructions that,when executed in hardware, perform a process comprising: receiving, froma data-sending protocol entity, a control protocol data unit, whereinsaid control protocol data unit identifies other protocol data unitsdestined to a data-receiving protocol entity; retrieving from thecontrol protocol data unit, for at least one of said identified protocoldata units, an indirect indication of at least one delay figure of adelivery path chosen for an initial transmission of the identifiedprotocol data unit, wherein the at least one delay figure ispreconfigured at bearer configuration, observing a gap in a sequence ofthe identified other protocol data units at reception; and applying theat least one delay figure to determine a waiting time in relation to thegap.